Weird curling problem when printing a thin item in 100% infil

[TT_Vert]

The print job is a 4.5mm thick plate (lid actually) that is 155x160mm (See attached stl). It will curl on the front right side of the print when printing infills of 50% or greater. Al though due to time constraints I only tested in 20% (my normal go to infill), 50% and 100% (What my goal infill for this job was)

• The printer is a maker select 2 that I've had for many years.
• The bed surface material was replaced a few months ago also but not because of this, just because it was years old.
• I am using the same filament I've been using for 2 rolls from amazon (SUNLU).
• I've had no other issues w/ this filament and reviews have been good
• I print at 210/40C and always have w/o any issues
• printer config:

• Maker Select 2
• I have a duct w/ a cage fan that cools prints. Print cooling fan is running after layer 2
• 210/40C
• 1st layer 15mm/sec
• all other layers 50mm/sec
• .28mm layer height
• 210/40C

print info and tests I've run on same job

• If I print the job at 50% infill it's better
• If I print the job at 20% infill it does not curl
• Tried to reduce printhead temp to 200, no change
• Bed is level to .001" as confirmed w/ a feeler gauge
• Bed is clear of any debris

I don't think it's pertinent here but I have included a copy of the item I was printing.